Muffler



De@ 21, 1 943- Q. G. NoBLlTT ET AL 2,337,299

MUFFLER Filed Sept. 2, 1941 (PRL-r unHn/nu n nuuuulnnn Mun uuuunnunn nunnunuu* ai ai L la@ il M LM ifatented Dec. 21, 1943 parte MUFFLER Quintin G. Noblitt and Edmund Ludlow, Columbus, Ind., assignors to Noblitt-Sparks Industries, Inc., Columbus, Ind., a corporation of Indiana Application September 2, 1941, Serial No. 499,238

5 Claims.

Our invention relates to silencers, and particularly to silencers for use in silencing the exhaust of internal-combustion engines. It is our object to produce silencers which can be simply and economically manufactured, which will possess an effective silencing action, and which will produce a relatively low back pressure.

In practicing our invention, we subject the gases to the action of side silencing chambers, both tuned and untuned. ln addition, we divide the gases into two or more components, cause the components to flow over paths of diierent lengths, and then recoinbine them to silence sounds of more or less definite wave lengths as the result of interference eiects. Desirably, the gases are subjected to the action of the untuned side silencing chambers before being divided.

The accompanying drawing illustrates our invention, Fig. l being a longitudinal section through a silencer and Fig. 2 a transverse section on the line 2-2 of Fig. l.

The muffler illustrated in the drawing cornprises a cylindrical shell Il! which, as indicated in Fig. 2, is conveniently of a general elliptical shape in cross-section, but which may have any convenient cross-sectional form. The front and rear ends of the shell it are closed respectively by heads l! and i2. Spaced longitudinally from these heads and from each other are two transverse partitions i3 and i4 through which there extend three tubes it, it, and il. The iront end of one of these tubes, here shown as the tube l5, is connected to an inlet nipple i3 which extends through the front head li and is adapted at its front end for connection to the exhaust pipe er" an internal combustion engine. Another of the tubes, shown as the tube i6, communicates at its rear end with an exhaust nipple i9 which projects rearwardly through the head l2 and is adapted at its rear end for connection to a suitable tail pipe.

Between the iront i i and the partition i3 we mount a transverse partition 2! which cooperates with the head I! to define a silencing chamber and with the partition i3 to define a transverse passage interconnecting the front ends of the tubes l and il'. A similar partition 24 near the rear of the casing i3 Ico-operates with the ii to deiine a second silencing chamber and with the partition Hl to denne a transverse interconnecting the rear ends ci the tubes l5 and Il.

Extending through the partition 2i is a tube 3l) providing a restricted neck through which the silencing chamber 22 communicates with the passage 23. A similar tube 3l extending through the partition 24 provides communication between the silencing chamber 25 and the passage 2S. As is well known each of the chambers 22 and i5, with its associated neck Se or 3i, serves to absorb sounds of more or less denite frequency depending upon the volume of the chamber and upon the cross-sectional area and length of the neck.

As will be clear from Fig. l, the tube is provided with a multiplicity of perioraticns entending throughout its length, such perforations desirably being in the form oi narrow, circtunieientially extending slots 33. The space between the partitions i3 and I4 is preferably divided into a plurality of silencing chambers 3d, and 3l by transversely extending partitions S5.

Between the partitions I4 and 23, the conduit formed by the tube if? and the outlet nipple lil is provided with a more or less restricted opening through which gases from the passage may enter such conduit and be discharged through the outlet nipple ill without passing through the tubes l'i and I6. Desirably, to provide this opening, the nipple i9 extends forwardly beyond the partition 24, while the rear end or the tube l extends into the front end of the nipple le is slightly reduced in diameter to provide annular opening indicated at 4l! in Fig, l.

In the operation of the fouiller above described, the exhaust gases enter the front end of the tube I5 through the nipple i8. As they pass through the tube I5, some of the gases in high-pressure zones pass outwardly through the openings into the side chambers 34, 35, and 3l and return to the tube when low-pressure zones pass therethrough. Thus, the chambers S5., 35, and 3l act as untuned, or as relatively broadly tuned, side silencing chambers tending to suppress sounds over a fairly wide range of frecuen es.

Leaving the tube i5, the gases enter the transverse passage 2B in which they divide into two components one of which hows directly through the annular opening 40 into the discharge nipple i9 while the other flows through the tube 5'?, transverse passage 23, and tube iE into the discharge nipple. Because of the difference in the lengths of the paths followed by the two coinponents, interference effects occur where the coi-M ponents are recombined in the discharge nip c i9, thus tending to silence sounds of more or ....s definite frequency depending upon the di in the lengths of the paths.

As previously noted, the arrangement of slots 33 and chambers Sii, 35, 3S, and 3i tends to suppress sounds over a fairly broad band of frequencies, While the tuned chambers 22 and 25 and the interference phenomena occurring within the conduit iti-IS adjacent the opening di! tend to suppress sounds of more or less denite frequency. Various considerations, including limitations upon the size ci the silencer, restrict to some extent the frequencies which can eiectively be suppressed by the respective silencing instrumentalities incorporated in our muffler. Generally, the arrangement of slots 33 and chambers 34 to 3l is adapted to suppress a broad band of relatively high frequencies-say frequencies of the order of 500 to 1500 per second. Silencing chambers, such as the chambers 22 and 25, are adapted to suppress relatively low frequenciessay frequencies below 250 per second. In a murder of a size suitable for use in an automobile, the interference phenomena within the conduit iii-i9 will serve to suppress a more or less definite frequency within an intermediate range-say the range from 250 to 5Go per sec- The frequency suppressed by the interference phenomena can be controlled by regulation of the length of the gas-path through the Itubes it and il'.

it will be noted that the gases which directly enter the nipple it iro-rn the passage 2t through the annular opening it are not subjected to the action of the silencing chamber 22 at the front end oi the muiiler and that the silencing cham- 25 will have little if any eiiect upon them. We have found, however, that if the entire stream of gases entering the silencer is first subjected to the action of a silencing instrumentality, such as the arrangement of slots 33' and chambers 3ft to 3l', which tends to suppress a fairly broad band of relatively high frequencies a substantial portion of the gases may then be conducted directly to the outlet, as through the opening fill, without being subjected to the action of low-frequency suppressing means; and that no objectionable decrease in the silencing action will thereby result. In other words, so long as all the gases are subjected to the action of a high-frequency suppressing means, silencing eiiectiveness will not be materially reduced if only a portion of them is subjected to the action or low-frequency suppressing means. Moreover, permitting a portion of the gas stream to enter the discharge nipple directly after passing through the tube EE and without'passing through the tubes ifi and il reduces the back pressure which the silencer would otherwise create.

The provision of the opening t@ thus results in two advantages; for it not only reduces back pressure but also results in the creation of interference phenomena which can be availed of to suppress a more or less definite predetermined frequency lying within a range which other instrumentaiities oi the silencer are less well adapted to suppress.

In our copending application, Seial No. 499,239, have disclosed another form of silencer enibod, ing the subject matter broadly claimed herein.

We claim as our invention:

l. In a silencer, an elongated casing having iront and rear ends, a pair of main transverse partitions disposed in said casing and spaced *from the ends of the casing and from each other, three tubes extending longitudinally oi the casing between said main partitions, a conduit for conveying gases to the front end of the rst of said tubes, said first tube being provided between said partitions with a multiplicity of longitudinally distributed openings providing restricted communication between such rst tube and the space between said partitions and within the casing, means providing a rear transverse passage interconnecting the rear end of said first tube and the rear end of the second of said tubes, means providing a iront transverse passage interconnecting the front ends of the second and third tubes, a conduit extending through said rear transverse passage for conveying gases from the rear end of said third tube, said conduit having an opening permitting gases to enter it from said rear transverse passage, and a tuned silencing chamber communicating with each or1 said transverse passages.

2. in a silencer, an elongated casing having liront and rear ends, a pair of main transverse partitions disposed in said casing and spaced from. the ends of the casing and from each other, e tubes extending longitudinally of the casbetween said main partitions, a conduit for conveying gases to the iront end of the first oi said tubes, said iirst tube being provided between said pa tions with a multiplicity of lcngitudie naliy distributed openings providing restricted communication between such first tube and the space between said partitions and within the "asing, means providing a rear transverse paslage interconnecting the rear end of said first tbe and the rear end of the second of said tubes,

providing a iront transverse passage inird tubes, a conduit extending through said ear transverse passage for conveying gases from .aving an opening permitting gases to enter it from said rear transverse passage, and a tuned silencing chamber communicaiinCT with one of u transverse passages.

3. The invention set forth in claim 2 with the addition that the iront end of said last named conduit is disposed within said rear transverse passage and telescopically receives the rear end oi said third tube, the iront end of such conduit being larger than the rear end of said hird tube to provide the opening through which gases from the rear transverse passage enter such conduit.

4. In a silencer, an elongated casing having iront and rear ends, a pair of main transverse partitions dispose in said casing 4and spaced from the ends of the casing and from each other, three tubes extending longitudinally ci the casing between said main partitions, a conduit for conveying gases to the front end of the first of said tubes, said iirst tube being provided between said partitions with a multiplicity cf longitudinally distributed openings providing restricted communication between such iirst tube and space between said partitions and within the casing, means providing a rear transverse passage interconnecting the rear end of said rst tube and the rear end of the second of said tubes, means providing a iront transverse passage interconnecting the iront ends of the second and third tubes, a conduit extending through said rear transverse passage for conveying gases from the rear end of third tube, said conduit having an opening permitting gases to enter it from said rear transverse passage, and means asso-- cated with each of said transverse passages for suppressing low-frequency sounds.

5. In a silencer, an elongated casing having front and rear ends, a pair of main transverse partitions disposed in said casing and spaced tube and the rear end of the second of said tubes, from the ends of the casing and from each other, means providing a front transverse passage int `ee tubes extending longitudinally of the casterconnecting the front ends of the second and ing between said main partitions, a conduit for third tubes, a conduit extending through said conveying gases to the front end of the first of rear transverse passage for conveying gases from said tubes, said rst tube being provided between the rear end of said third tube, said conduit havsaid partitions with a multiplicity of longitudiing an opening permitting gases to enter it from nally distributed openings providing restricted said rear transverse passage, and means assocommunicaton between such first tube and the ciated with one of said transverse passages for space between said partitions and within the 10 suppressing low-frequency sounds.

casing, means providing a rear transverse pas- EDMUND LUDLOW.

sage interconnecting the rear end of said irst QUINTIN G. NOBLITT. 

